Precise Control of the Molecular Arrangement of Organic Semiconductors for High Charge Carrier Mobility

Organic semiconductors are well-known to exhibit high
charge carrier
mobility based on their spread of the π-orbital. In particular,
the π-orbital overlap between neighboring molecules significantly
affects their charge carrier mobility. This study elucidated the direct
effect of subtle differences in the π-orbital overlap on charge
carrier mobility, by precisely controlling only molecular arrangements
without any chemical modifications. We synthesized disulfonic acid
composed of a [1]benzothieno[3,2-b][1]benzothiophene
(BTBT) moiety, and prepared organic salts with four butylamine
isomers. Regardless of the type of butylamine combined, electronic
states of the constituent BTBT derivative were identical,
and all BTBT arrangements were edge-to-face herringbone-type.
However, depending on the difference of steric hindrance, center-to-center
distances and dihedral angles between neighboring BTBT moieties slightly varied. Despite a similar arrangement, the photoconductivity
of four organic salts differed by a factor of approximately two. Additionally,
theoretical charge carrier mobilities from their crystal structures
exhibited a strong correlation with their photoconductivity.